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Additive effects of marine protected areas and land-use on inter- and intraspecific trait variability in tropical seagrass assemblages
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.ORCID iD: 0000-0002-3973-1703
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Marine ecosystems are under increasing human pressure and therefore in need of effective management. Marine protected areas (MPAs) can reduce effects of local disturbances (e.g. fishing), but their ability to buffer stressors originating outside MPA borders (e.g. runoff) is more unclear. Moreover, while MPAs are well-known to affect species composition, we know much less about their effects on organisms’ traits (physiological, morphological, and/or behavioural characteristics), which in turn dictate how organisms respond to stressors and influence ecosystem processes and services. Here, we conducted a field survey in southern Kenya to assess the single and joint (interactive) effects of MPAs and land-use on species and trait composition of seagrass assemblages; a key group of habitat-forming plants in shallow coastal areas. We measured five morphological traits on multispecies seagrass assemblages (leaf length and width, number of leaves per shoot, and above- and below-ground biomass) within three types of sites: government-managed MPAs, community-managed MPAs, and unprotected areas. Using single- and multi-trait statistical analyses, we found that both MPAs and land-use influence seagrass species and trait composition. Changes in community-level traits were mostly explained by species turnover. However, management and land-use also had a direct influence on trait composition, with MPAs promoting wider leaves and higher above-ground biomass, while land-use mostly influenced seagrass leaf length and below-ground biomass. Moreover, even though there was an interactive effect of management and land-use, the largest and oldest MPAs did not seem to buffer effects of intense land-use. In conclusion, it appears that MPAs influence seagrass assemblages by reducing local disturbances, but do not buffer spatially distant land-use effects. Consequently, to sustain seagrass ecosystems and the important services they support, there is a need for a more integrated coastal zone management that regulates resource use and human impacts in both the marine and the terrestrial parts of tropical coastal zones.

National Category
Biological Sciences
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-154962OAI: oai:DiVA.org:su-154962DiVA, id: diva2:1196071
Available from: 2018-04-09 Created: 2018-04-09 Last updated: 2018-04-10Bibliographically approved
In thesis
1. Effects of Marine Protected Areas on Tropical Seagrass Ecosystems
Open this publication in new window or tab >>Effects of Marine Protected Areas on Tropical Seagrass Ecosystems
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Seagrass beds are highly productive coastal ecosystems that sustain a rich and diverse associated fauna and flora. Increasing anthropogenic pressures threaten seagrass ecosystems and have already led to major seagrass losses across the world. Marine Protected Areas (MPAs) have become one of the key strategies to manage coastal ecosystems and associated resources worldwide and have been often shown to successfully protect marine ecosystems. However, relatively few studies have assessed the effects of MPAs on seagrass ecosystems, and there are indications that MPAs may not be able to fully protect seagrasses, especially from disturbances originating outside their boundaries. Within this context, this thesis aimed to investigate the direct and indirect effects (those mediated by biotic interactions) of MPAs on tropical seagrasses, associated fish communities, and ecosystem processes.

The thesis consists of three parts. First, we used 10-years of seagrass monitoring data within a MPA to evaluate the temporal variability in seagrass cover and species composition in relation to changes in environmental conditions (Paper I). Second, we investigated the potential of MPAs to enhance the temporal stability of seagrass ecosystems using a 10-month field study. We surveyed seagrass-associated fish communities (Paper II) and estimated seagrass growth and herbivory rates (Paper III) during three different seasons within MPAs and unprotected sites. Finally, to evaluate the effects of MPAs and land-use on seagrass ecosystems we surveyed seagrass species and trait composition within government-managed MPAs, community-managed MPAs, and unprotected sites (Paper IV).

The seagrass bed monitored in Paper I showed a high temporal and spatial variability, with a temporal decline in cover and change in species composition, followed by a period of recovery. This pattern could not be associated with any of the climate and tidal variables considered, suggesting that potential drivers of decline may have originated outside MPA boundaries. The results from the seasonal field study showed that MPAs increased the temporal stability of seagrass-associated fish communities, particularly juvenile fish (Paper II), and strengthened a positive link between herbivorous fish, herbivory rates, and seagrass growth (Paper III), suggesting the presence of a positive feedback that promotes stability. Finally, MPAs affected seagrass species and trait composition (by selecting for more stress-sensitive species) but did not seem to be able to protect seagrasses from land-use effects, with seagrasses showing similar changes in species and trait composition within and outside MPAs (Paper IV). Considering these results, this thesis builds to a body of literature indicating that MPAs alone may not be sufficient to protect seagrass ecosystems and that improved management strategies may be necessary to preserve these important coastal habitats.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2018. p. 54
Keywords
coastal ecosystems, seagrass, marine protected areas, management, conservation, fish, herbivory, Western Indian Ocean, East Africa, tropical
National Category
Biological Sciences Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-154966 (URN)978-91-7797-268-6 (ISBN)978-91-7797-269-3 (ISBN)
Public defence
2018-06-05, Vivi Täckholmssalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, Stockholm, 09:30 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2018-05-09 Created: 2018-04-09 Last updated: 2018-05-04Bibliographically approved

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